High-Temperature Plug Formation With Silicates

Abstract

Abstract A grouting system is being developed that is applicable to water shutoff, steam flooding, and high-temperature grouting/plugging for lost circulation. This grouting system uses silicate hydrates as the plugging material. We describe a means to introduce sodium silicate and an activator through a single tubular by encapsulating the activator in a material that is temperature sensitive, thus delaying the initiation of the reaction. The formation of silicate hydrate plugs has been studied over the range of 80°C to 300°C as well as the chemical stability of silicate hydrate for 10–12 weeks. Introduction This work describes a chemical solution of exploiting silicates' unique gelling properties in an environmentally friendly and cost-effective way to form plugs for use in water shutoff strategy, steam flooding, and high-temperature grouting/plugging for lost circulation. Silicates have been used to form stable grouts and cements for over 50 years because of their ability to gel and polymerize. This reaction has also been used successfully for water shutoff and to solve lost-circulation problems in oil and gas drilling that require a plug to be formed at various weak spots in a well formation. The reaction happens in seconds to minutes (generally controlled by the mixing rate). In addition to their gelling action, silicates will also react with soluble metal salts, such as calcium chloride, to produce insoluble metal silicate hydrate plugs. The need for this work arose primarily from geothermal drilling research wherein we are faced with severe lost-circulation problems, often at elevated temperatures. This paper summarizes current laboratory-based advances in developing high-temperature plugs for lost-circulation zones. The purpose of this research includes developing emplacement systems and determining the temperature limits of reactive plugs for cross flow. Sandia National Laboratories, with support by the Geothermal Technologies Program of the U.S. Department of Energy has studied wellbore integrity in geothermal environments. A portion of wellbore integrity research has been directed towards developing materials and methods of solving lost circulation problems in a cost-effective way. Geothermal environments are hot, with temperatures in the range of 80°C to 300°C, and are possibly laden with water, brine, etc. In severe lost-circulation situations, cross flow may be experienced, in which pressure-induced fluid flow may occur through a borehole. When lost circulation of drilling fluid is experienced in geothermal wells, cement plugs are a common initial solution to the problem. A typical procedure would be to stop drilling, place the cement plug and allow the cement to cure, then re-drill. However, high cross-flow rates and/or large voids, many fractures, and high porosity/permeability zones can present difficult circumstances for conventional cement plug deployment. For example, cement can be washed out or migrate away from the zone of interest due to unbalanced hydrostatic pressures before it has set, or the amount of placed cement may not fill all of the voids present. For water shutoff and to control flow in steam flooding, the problem is slightly different.In these situations, the grout must flow in fractures or through a permeable zone, filling it, to seal a large volume. Through a systems approach, we are investigating materials that can be created and will survive in a geothermal environment without degrading. The chemistry as well as the "mechanical survivability" of the materials at geothermal conditions has been studied, initially through lab and planned bench-scale and field-testing. Awareness of a reasonable downhole deployment scheme must be factored into early material development work. Materials considered must be environmentally suitable and the total costs of the material's deployment process must be economic, realizing that down time caused by lost circulation is very costly.